1. Field of the Invention
The present invention relates to a development device, a process cartridge, and an image forming apparatus using the development device, and more particularly, to a development device with enhanced mixing performance which can effectively supply particulate material for mixing into electrophotographic developer, and a process cartridge and image forming apparatus incorporating such a development device.
2. Discussion of the Background
Electrophotographic image forming apparatuses, such as printers, photocopiers, and facsimiles, typically implement a development system for developing an electrostatic latent image formed on a photosensitive surface into a visible image. In electrophotographic image formation, development is performed using a developer material which is typically a mixture of toner and carrier particles. A development device or a process cartridge incorporating a developing feature includes a developer reservoir that provides a developer mixture to a developer roller for applying toner to the photosensitive surface.
In a common configuration, the developer reservoir has a mixing chamber in which an agitating member such as a screw conveyor agitates and conveys the developer mixture toward the developer roller. As the developer becomes depleted of toner through use, the developer reservoir receives new toner at a toner inlet located on an upper side of the mixing chamber. The toner supply is dispensed to fall onto the surface of contents of the mixing chamber.
Such a configuration is less reliable in mixing developer sufficiently and uniformly, however. As toner typically has a low relative density with respect to developer containing magnetic carrier particles, toner particles supplied from above tend to glide or flow over the surface of the existing developer particles. Insufficient mixing degrades homogeneity in toner concentration and causes various defects due to poorly charged toner particles, such as toner scattering on prints and/or toner contamination inside the machine. In particular, when the gliding toner reaches a portion adjacent to the developer roller in the mixing chamber, the poorly charged particles may result in non-uniform areas present on corresponding parts of developed images. Such a problem becomes serious when the development device features compact size and enhanced operating speed, which typically involves difficult conditions for developer mixing, for example, increasing the amount of toner dispensed at a time, or reducing the size of the agitating member used in the mixing chamber. Not surprisingly, various methods have been proposed to improve mixing performance of development devices.
Referring to FIGS. 1A and 1B, cross-sectional side views schematically illustrating an example of a conventional development device 109 in different states are described.
As shown in FIG. 1A, the development device 109 includes a developer reservoir 114 defining first and second chambers 114a and 114b each supporting first and second screw conveyors 101 and 102, a developer roller 107, a toner inlet 119, and a toner guide 112. The first and second chambers 114a and 114b hold developer 113 including toner particles and carrier particles.
In the development device 109, a supply of toner is dispensed to the toner inlet 119 disposed on an upper side of the developer reservoir 114. The toner inlet 119 leads to a vertical guide path defined by the toner guide 112 at one side of the first chamber 114a. The supplied toner travels along the guide path to enter the first chamber 114a as the first screw conveyor 101 rotates in a direction of arrow X0.
The development device 109 is designed to effectively introduce the supply of toner into the developer 113, wherein the toner guide 112 is assumed to penetrate below a top surface of the contents of the first chamber 114a. However, such a method may be invalid or not reliable considering that the level or the position of the surface of the contents of the first chamber 114a changes as the development device 109 operates to transport and consume the developer 113 therewithin.
Thus, as shown in FIG. 1B, during operation, the rotation of the first screw conveyor 101 may move the contents of the first chamber 114a to a side away from the guide path, so that the top surface of the contents slopes down toward the lower end of the toner guide 112. As a result, the toner exiting the guide path falls down onto a lower portion of the sloping surface and glides thereover without mixing into the developer 113 therebeneath. The developer 113 insufficiently mixed may not offer acceptable performance in developing electrophotographic images.
Accordingly, there is a need for a development device with enhanced mixing performance which can effectively and reliably supply particulate material for mixing into electrophotographic developer. An electrophotographic system incorporating such an apparatus may produce high quality images with desirable uniformity while reducing defects due to poorly charged toner particles.